Switching voltage regulator circuit

ABSTRACT

A tapped inductor is utilized in a switching mode voltage regulator, which employs a pass transistor and an associated driver transistor connected in a modified Darlington configuration, for the purpose of allowing these transistors to saturate during switching, thereby substantially increasing the over-all efficiency of the regulator. A filter circuit may be added at the output of the voltage regulator to significantly reduce ripple and to improve the response of the regulator to load transients.

United States Patent 11 1 1111 3,781,654 Simcoe Dec. 25, 1973 [54] SWITCHING VOLTAGE REGULATOR 3,328,674 6/1967 Bleicher 323/DIG. 1

CIRCUIT FOREIGN PATENTS OR APPLICATIONS [75] Inventor: K nt W- i Loveland, Colo- 1,939,459 2 1970 Germany 323 1310. I [73] Assignee: Hewlett-Packard Company, Palo Alto, Calif Prrmary Exammer-A. D. Pellmen AttorneyRoland l. Grifiin [22] Filed: May 26, 1972 [21] Appl. No.: 257,264 [57] ABSTRACT A tapped inductor is utilized in a switching mode volt- 52 us. 01. 323/17, 323/22 T, 323/1310. 1 age regulator which P Y a P transistor and an 51 1111. CL. 0051 1/56 associated driver transistor connected in a mOdified 58 Field of Search; 321/2; 323/17, 22 T, Darhhgtoh cohfigurahm, the Purpose of allwihg 323/38 DIG 1 these transistors to saturate during switching, thereby substantially increasing the over-all efficiency of the [56] References Cited regulator. A filter circuit may be added at the output UNITED STATES PATENTS of the voltage regulator to significantly reduce ripple and to improve the response of the regulator to load 3,417,321 12/1968 Clapp .1 323 1310. 1 transients 3,093,790 6/1963 Ehret 323/DIG. l 3,378,758 4/1968 Goodenow 323/DlG. l 3 Claims, 3 Drawing Figures SOURCE OF 46 UNREGULATED U 0. C. VOLTAGE PATENTEDuaczs I975 E 3,781,654

SOURCE OF UNRECULATEO D. C. VOLTAGE 1 19/0 Al T SOURCE OF UNRECULATED D. C. VOLTAGE SOURCE OF v UNRECULATEO D. C. VOLTAGE SWITCHING VOLTAGE REGULATOR CIRCUIT BACKGROUND AND SUMMARY OF THE INVENTION to operate properly, a significant amount of ripple is re quired on the feedback signal, which in turn has meant high ripple content at the output, thus preventing their use in a number of critical applications. Also, the transient response of these circuits to load fluctuations is poor because of low output capacitance. This situation exists because the output capacitance typically forms a portion of the timing circuitry. lt would be desirable to provide a circuit having timing circuitry which is independent of output capacitance.

Accordingly, it is the principal object of this invention to provide an improved switching regulator power supply circuit utilizing a minimum number of components and having high over-all efficiency.

It is a further object of this invention to provide an improved switching regulator power supply circuit which exhibits low ripple content at its output.

It is a further object of this invention to provide an improved switching regulator power supply circuit which has a better transient response to load variations than those circuits constructed according to the prior art.

DESCRIPTION OF THE DRAWINGS FIG. 1 is a detailed schematic diagram of a switching regulator circuit.

FIG. 2 is a detailed schematic diagram of a switching regulator circuit incorporating a filter for isolation of an output sense point according to the preferred embodiment of this invention.

FIG. 3 is a detailed schematic diagram of a switching regulator circuit utilizing an alternate configuration for the filter contained in the circuit of FIG. 2.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. 1, there is shown a prior art switching regulator circuit including a source of unregulated DC. voltage 10 connected to the input of a switching voltage regulator circuit. Such a source of input voltage may comprise, for example, a conventional -hertz transformer, a bridge rectifier, and a simple capacitive filter. A switching transistor 12 and an associated driver transistor 14 are connected as a modified Darlington pair with resistors 16 and 18 interposed between the respective bases thereof and the source of unregulated voltage to provide a discharge path for the bases. The emitter of switching transistor 12 is also returned to the source of unregulated voltage 10. The collector of transistor 12 is connected serially with an iron core inductor 20 to an output terminal 29. The

collector of transistor 14 is returned to a tap on inductor 20 through a resistor 22. This tap is positioned for providing sufficient voltage to saturate transistors 12 and 14 during switching, thereby significantly reducing the conduction losses therein. Tapped inductor 20 could be replaced with a resistor for generating this re quired voltage, but such an arrangement would result in the disadvantage of sizeable additional power losses. Resistor 22 is interposed between the tapped inductor 20 and the collector of transistor 14 to limit the maximum base current to transistor 12. Power dissipation in resistor 22 may be minimized by positioning the tap on inductor 20 consistent with transistor parameters and circuit requirements. A linear differential amplifier 24 is employed to provide base drive for transistor 14. Such an amplifier might comprise, for example, a Fairchild 723 integrated circuit operational amplifier, available as an off-the-shelf component. An inverting input 26 of amplifier 24 is connected to the point at which it is desired to sense the output of the voltage regulator. A non-inverting input 28 is connected through a resistor 30 to the collector-of transistor 12 and through another resistor 32 to a source of reference voltage 34. These resistors provide sufficient hysteresis to insure reliable switching, thus stabilizing the switching frequency and, hence, the switching losses. A diode 36 serves to clamp the input of inductor 20 to ground potential when transistors 12 and 14 are switched off. A capacitor 38 is provided at the output of the voltage regulator for ripple reduction.

Since hysteresis has been added to the circuit, a significant ripple signal at the switching frequency must be present on the feedback sense signal to amplifier 24. This requirement limits the amount of capacitance that can appear at the output of inductor 20, thus limiting the size of capacitor 38 and, hence, the purity of the regulator output and the transient response of the regulator circuit.

Referring now to FIG. 2, there is shown the prior art circuit of FIG. 1 with the addition of a filter for isolating the output sense point from the remaining circuitry in accordance with the preferred embodiment of this invention. By providing such isolation, an output capacitor 42 may be made very large, thus significantly reducing the ripple content of the regulated output voltage and improving the response to load transients. The filter comprises a transformer 40 having a first winding connected between the output of inductor 20 and the output terminal 29 of the voltage regulator. A

second winding of the transformer is connected between the inverting input 26 of amplifier 24 and the point at which it is desired to sense the DC. output of the voltage regulator. The necessary ripple signal is thereby added to the D.C. sense signal by the second winding to insure proper operation of the circuit.

Referring to FIG. 3, there is shown the circuit of FIG. 2 in which an alternate configuration for the output filter has been implemented. Transformer 40 inFIG. 2 may be replaced by an iron core inductor 44 in FIG. 3. A capacitor 46 and a resistor 48 are provided to couple the total feedback signal comprising (1) the ripple signal appearing at the output of inductor 20 and (2) the DC. sense signal taken from the output of the voltage regulator to the inverting input 26 of amplifier 24.

I claim:

1. An improved switching circuit for deriving a regulated DC. voltage from a source of unregulated D.C.

voltage, said switching circuit being of the type having at least a switching transistor, an associated driver transistor, a linear differential amplifier with an inverting input for sensing the output voltage at an output of the switching circuit, with a non-inverting input for sensing a source of reference potential, and with an output for driving the switching and driver transistors, and a tapped inductor connected between the collector of the switching transistor and the output of the switching circuit, wherein the improvement comprises a transformer having a first winding connected between the tapped inductor and the output of the switching circuit and a second winding connected between the output of the switching circuit and the inverting input of the linear differential amplifien 2. An improved switching circuit for deriving a regulated D.C. voltage from a source of unregulated DC voltage, said switching circuit being of the type havng at least a switching transistor, an associated driver transistor, a linear differential amplifier with an inverting input for sensing the output signal at an output of the switching circuit, with a non-inverting input for sensing a source of reference potential, and with an output for driving the switching and driver transistors, and a tapped inductor connected between the collector of output of the switching circuit and associated means for coupling a feedback signal comprising both a ripple signal appearing at the point of connection of the tapped inductor and the filter inductor and a DC sense signal taken from the output of the switching circuit to the inverting input of the linear differential amplifier.

3. An improved switching circuit for deriving a regulated DC. voltage from a source of unregulated DC. voltage, said circuit being of the type having at least a switching transistor, an associated driver transistor, and a linear differential amplifier with an inverting input for sensing the output voltage at an output of the switching circuit, with a non-inverting input for sensing a source of reference potential, and with an output for driving the switching and driver transistors, wherein the improvement comprises a transformer having a first winding serially connected in an output lead of the switching circuit and a second winding connected between the output of the switching circuit and the inverting input of the linear differential amplifier. 

1. An improved switching circuit for deriving a regulated D.C. voltage from a source of unregulated D.C. voltage, said switching circuit being of the type having at least a switching transistor, an associated driver transistor, a linear differential amplifier with an inverting input for sensing the output voltage at An output of the switching circuit, with a non-inverting input for sensing a source of reference potential, and with an output for driving the switching and driver transistors, and a tapped inductor connected between the collector of the switching transistor and the output of the switching circuit, wherein the improvement comprises a transformer having a first winding connected between the tapped inductor and the output of the switching circuit and a second winding connected between the output of the switching circuit and the inverting input of the linear differential amplifier.
 2. An improved switching circuit for deriving a regulated D.C. voltage from a source of unregulated D.C. voltage, said switching circuit being of the type havng at least a switching transistor, an associated driver transistor, a linear differential amplifier with an inverting input for sensing the output signal at an output of the switching circuit, with a non-inverting input for sensing a source of reference potential, and with an output for driving the switching and driver transistors, and a tapped inductor connected between the collector of the switching transistor and the output of the switching circuit, wherein the improvement comprises a filter inductor interposed between the tapped inductor and the output of the switching circuit and associated means for coupling a feedback signal comprising both a ripple signal appearing at the point of connection of the tapped inductor and the filter inductor and a D.C. sense signal taken from the output of the switching circuit to the inverting input of the linear differential amplifier.
 3. An improved switching circuit for deriving a regulated D.C. voltage from a source of unregulated D.C. voltage, said circuit being of the type having at least a switching transistor, an associated driver transistor, and a linear differential amplifier with an inverting input for sensing the output voltage at an output of the switching circuit, with a non-inverting input for sensing a source of reference potential, and with an output for driving the switching and driver transistors, wherein the improvement comprises a transformer having a first winding serially connected in an output lead of the switching circuit and a second winding connected between the output of the switching circuit and the inverting input of the linear differential amplifier. 